A private branch exchange (PBX) is a telephone network that serves a business or an office. A virtual PBX (vPBX) allows a business or office to be served by a PBX system hosted on remote servers. The service is provided through a combined voice network (e.g. telephone network) and data network (e.g. Internet). A vPBX typically involves one or more voice-over-IP (“VOIP”) servers, a call management program, a network, a gateway that links the voice network and data network, and one or more extensions. Conventional implementation of a vPBX system is not well suited for permitting mobile devices to send authenticated faxes.